Method of plating metals



Patented 16, 1931- UNITED STATES PATENT OFFIC WILLIAM E. WATKINS, OF NEW YORK, N. Y., ASSI G-NOR COPPER PLATE SHEET & TUBE COMPANY, OF NEW YORK, N. Y., A. CORPORATION OF NEW JERSEY METHOD OF PLATING- METAL-S 1T0 Draw-ing. Application filed May 29,

This invention relates to the plating of metal articles, such as sheets or strips of H011 or steel, and more particularly toe method of forming a plating of an alloy of two or' more metals on a metal base.

This invention may be understood by considering its application to the plating of iron or steel sheets. In the production of a nonferrous covering on a ferrous base, the present universal practice is to take the iron or steel sheets from the hot rolls of the rolling mill, and stack them in piles in a Mesta pickler crate operated bya plunger which moves the crate up and down in an acid solution until all of the iron oxide on the sheets has been removed. The crate containing the sheets or plates is then transferred to a bath of water 'where it is plunged up and down until the sheets have been thoroughly cleaned. The sheets are then stacked in piles on an iron car and covered with an inverted iron pot,

the interstices between the iron pot and the floor of the car being chinked with sand to prevent admission of air. The car with its piles of sheets is then pushed into what is commonl known as a box annealing oven,

which is eated from 1400 F. to 1800 F. at.

the roof and left there until the temperature ofthe sheets, if .full finished stock, has been raised to approximately 1150 F. This annealmg requires from 15 to 20 hou li sildepending upon the uge-of the sheets. e heat is then turned 0 and the room with [its contents allowed to coolsufiiciently to permit the removal of the car containing the sheets. Afterremoval from the annealing oven the sheets are cooled to a temperature at which they will not oxidize when the inverted pot cover is removed, which cooling requires from 20 to. 30 hours.

The above described operations are known as black pickling aridblack annealing. The latter operation is carriedout for the purpose of removing the stresses set up in the sheets by the rolling mill while being rolled from the sheet bar,- and to make them soft enough to be fabricated. After receiving this treatment, and, ifintended to be plated, the sheets are cold rolled for the purpose of giving them a fine-grained surface. This rolling 1929. Serial No. 367,125.

makes the sheets too hard to be fabricated and they must again be annealed and pickled before they can be plated, after which they until they "are taken out and passed through a bath of molten non-ferrous metal. These latter operations are known as white annealing and white pickling.

' The above described rocess, now'in universal use, is both ine cient and wasteful. For instance, in the black and white pickling operations reliance is placed on the repeated plunging of the pickler crate to separate the sheets sufliciently to permit -the acid to remove all of the oxide. In order to secure satisfactory results, the black pickling should be continued for approximately 4 minutes and the white pickling for approximately 2 minutes. This prolonged exposure of. the sheets to the action of the aci results in excessive loss of the ferrous metal. I- have found, in actual commercial practice, that by using my improved method, it is not necessary to expose the ferrous metal to the action of the acid for more than one minute, and,

the loss of ferrous metal 'is less than one-half annealing temperature is in the neighbor-.

hood of 1620 F. however, if an attempt were made to raise the temperature of a stack or pile of full finished sheets above 1150 F., the surfaces of the plates would become soft enough to-cause the sheets to stick together. The present invention makes it possible to subject each sheet to the proper annealing temperature, and being done singly the sheets cannot stick together.

According to the present invention, the sheets are given a preliminary treatment for the purpose of straightening them, for removing anyoxides present on the surfaces thereof, and for imparting to the sheets the desired surface characteristics. The sheets or strips are then ready for the plating 0 eration and a platingl of zinc is applied to the surfaces of the s eets or strips y conveyin them through a molten bath of zinc. In this manner a uniform plating film of zinc is arranged on the metal sheets or strips. The zinc plated sheet or strip is then coated with a liquid mixture containing finely divided copper particles. The coating mixture ma be applied by passing the sheets or strips t rough a coatingmpparatus such as is disclosed in my prior atent No. 1,295,820 and applying to the surfaces of the sheets or strips a suspension of finely divided copper particles in a suitable liquid spreading medium, such as an asphaltic base hydrocarbon oil. The zinc plated metal with the coating of copper applied thereto is then heated to a temperature below the volatilization point of zinc to cause the zinc of the plating to diffuse into the copper coating and form a brass coating. The brass coated strip is then through a second heating chamber at a 'gher tern rature and submitted to such conditions of time and temperature as will form a nonstripping, adherent plating of brass on the ferrous base.

In my copending application Serial No. 365,7 85, filed May 24, 1929, I have disclosed and claimed a process of plating a metal base, such as a ferrous sheet or strip, with a plating of an alloy in which the two or more metals to form the alloy are applied to the surfaces of the sheet or strip simultaneously in finely divided form by means of a suitablespreading vehicle such as an asphaltic base hydrocarbon oil. In my cotpliznding applications Serial No. 358,438 ed Apri 26, 1929, and Serial No. 366,087 filed May 25, 1929, I have disclosed and claimed procemes of forming a plating of an alloy on a ferrous base or strip in which a copper plating is first formed on a ferrous base, or a previously copper plated sheet or strip is coated with a mixture containing finely? divided zinc and the sheet or strip subsequently treated to form a plating of brass on the ferrous base. The present invention differs from the inventions of my copending applications in that the ferrous sheet or strip is first plated with zinc by passing it through a bath of molten zinc and a coating mixture containing finely divided particles of copper is then applied to the surfaces of the zinc plated strip;

e first step of the process of the present invention consists in passing the ferrous sheet or strip through a molten bath of zinc to form a plating of zinc on the sheet or strip. The zinc plated sheet or strip is then coated with a mixture containing finely divided copper. As stated above the copper coating can be applied to the sheet or strip by passin the sheet or stri through a coating machine of the type s own in my Patent No. 1,295,820. In general, this coating machine includes a mixing tank and a air of coating rolls between which the flat s eets or strips may be passed to receive the viscous composition containing the finely divided copper in suspension. The mixing tank contains an agitator for maintaining the roper homogeneity of the composition an means is provided for pumpin the agitated composition from the tank an spreading it on each of the coating rolls in a substantially uniform ayer.

The sheets to which the mixture has been applied are then first heated to a temperature su cient to secure the; diffusion of the zinc into .the co per and form brass and are subsequently lieated to a plating temperature to form a nonstripping, adherent plating of brass on the ferrous base. The heat treatments may be carried out in any suitable apparatus ,but I prefer to employ the furnace described and claimed in my prior Patent No. 1,67 9,389. The a paratus therein described eomprises a pre 'minary heating zone and a main heating zone. This construction permits a low temperature to be carried in the preliminary heating zone and a. higher temperature in the main heating zone. The length of the preliminary heating zone may be proportioned to the contemplated speed of travel of the material to obtain the desired heat treatments in each part of the furnace. I preferably so control the furnace and the speed of travel of the material to secure a temperature of 500-550 C. in the preliminary heating .zone which causes the zinc plating to diffuse into the copper of the second coating mixture and form rass. When the brass coated sheet or strip is passed through the main heating zone of the furnace, it is subjected to a temperature of from 900 to 1200 C. and forms a non-strippin adherent platingeof brass on the ferrous se. The brass, ing formed before the metal is assed into the main heating zone will not unfavorably affected by the temperatures empk iyedin the plating he vehicle employed or the purpose of spreading the finely divided material uniformly over thesheets, ma be any suitable liquid, preferably of a ucing character. 011, having an asphaltic base,'is particularly suitable; and I have found that Mexican or Oklahoma crude petroleum having a specific avit corresponding to 7 to poun s to .t e gallon gives very satisfactory results. This crude o1l possesses the desired spreading pro erties and the ability to hold t e finely divi ed material in suspension; and its viscosity, reducing characteristics and cheapness render it particularly valuable for this purpose. In the event that a non-reducing vehicle is employed, I prefer to incorporate a reducin agent, such as finely divided carbon, the re ucing agent being thoroughly mixed with the liquid and the plating material. Even when a reducing vehicle is employed, it is oftentimes desirable to add a small quantity of a reducing agent to supplement the reducing action of the vehicle. A mixture having the proportions of 1 ounce of carbon to one pound of finely divided plat- 10 ing mixture and one pound of Mexican petroleum gives desirable results.

I claim:

1. The method of forming a plating of an alloy of two or more metals on a metal base 1 which comprises passing the metal to be plated through a molten bath of one of the metals of the alloy to form a plating on the metal base, applying a plating mixture of the second metal to the plated metal, heating go the coated metal to cause one of the metals of the alloy to difluse into the other and form a coating of the desired alloy, and then subjecting the coated metal to a temperature sufiicient to form a ion-stripping plating of 25 the alloy on the metal base.

2. The method of forming a plating of brass on a ferrous base which comprises passing ferrous metal through a bath of molten zinc to form a zinc plating thereon, applyin a a coating mixture containing finely divided copper to the zinc plated ferrous metal, heating the coated metal to a temperature below the volatilization point of zinc to form a brass coating on the ferrous base, and then heating 8 the brass coated metal under such conditions of time and temperature as will cause the formation of an adherent, non-stripping plating of brass on the metal base.

3. The method of forming a plating of w brass on a ferrous base which comprises passing ferrous metal through a bath of molten zinc to form a zinc plating on the ferrous base, applying a coating mixture containing finely divided copper to the zinc plated fer- 48 rous metal, heating the coated metal to a temperature of 500-550 C. to cause the zinc of the plating to diffuse into the copper and form a brass coating and then heating the brass coated metal to a temperature of i0 9001200 C. to form a non-stripping, ad-

herent platin of brass on the ferrous metal.

4. The method of forming a plating of brass on a ferrous base which comprises forming a. plating of zinc on the ferrous metal,

55 applying a. coating mixture containing finely divided copper to the zinc plated ferrous metal, heating the coated metal to a temperature below the volatilization point of zinc to cause the zinc to diffuse into the copper and form a brass coating, and then heating the coated metal to a temperature sufficient to form a non-stripping, adherent plating of brass on the ferrous base.

In testimony whereof I afiix my signature.

WILLIAM E. WATKINS. 

